1. Field of the Invention
The present invention relates in general to a variable valve system of an internal combustion engine, which is able to vary a lift degree (or work angle) of engine valves (viz., intake and/or exhaust valves) in accordance with an operation condition of the engine. More specifically, the present invention relates to such variable valve system and a method of assembling the same.
2. Description of the Related Art
Hitherto, in the field of variable valve systems of an internal combustion engine, various types have been proposed and put into practical use. One of the systems is shown in U.S. Pat. No. 6,615,777.
The variable valve system of this US patent generally comprises a valve lift varying mechanism that, by rotating a control shaft, varies a lift degree (or work angle) of engine valves (viz., intake and/or exhaust valves) and an actuating mechanism that drives or rotates the control shaft in accordance with an operation condition of the engine.
The actuating mechanism comprises an electric motor, an output shaft driven by the electric motor, a screw nut having an inner thread meshed with an outer thread formed on the output shaft, a link member having a forked end pivotally connected to diametrically opposed portions of the screw nut through bearing pins and a lever member having one end pivotally connected to the other end of the link member and the other end rotatably connected to the control shaft through a pin. The control shaft has adjusting cams integrally connected thereto.
When, upon energization of the electric motor, the output shaft is rotated about its axis, the screw nut is moved axially forward or rearward along the output shaft pivotally moving both the link member and the lever member. With this, the control shaft is turned about its axis to a desired angular position.